P4879 - 幸运数字

内存限制：256 MB 时间限制：1 S 标准输入输出

题目类型：传统评测方式：文本比较上传者：

提交：19 通过：9

IT城税务局新大楼内所有办公室的号码将有幸运数字。
幸运数字是一个仅由数字 7 和 8 组成的数字。找到税务局新大楼中办公室的最大数量，因为门牌可以容纳不超过n位数字的数字。

The numbers of all offices in the new building of the Tax Office of IT City will have lucky numbers.

Lucky number is a number that consists of digits 7 and 8 only. Find the maximum number of offices in the new building of the Tax Office given that a door-plate can hold a number not longer than n digits.

Input

The only line of input contains one integer n (1≤n≤55) − the maximum length of a number that a door-plate can hold.

Output

Output one integer − the maximum number of offices, than can have unique lucky numbers not longer than n digits.

Examples

Input

Output

The only line of input contains one integer n (1≤n≤55) − the maximum length of a number that a door-plate can hold.

Output one integer − the maximum number of offices, than can have unique lucky numbers not longer than n digits.

630C 1100 combinatorics, math 思维

4879: 幸运数字

题目描述

输入格式

输出格式

输入样例复制

输出样例复制

分类标签